This interpretive section, I believe, falls within vv.17-48. Vv. 17-19 introduce the topic, which is the correct teaching of the law. The correct teaching is summarized in v. 48: Ἔσεσθε οὖν ὑμεῖς τέλειοι ὡς ὁ πατὴρ ὑμῶν ὁ οὐράνιος τέλειός ἐστιν. Further, the contrastive pair Ἠκούσατε ὅτι ἐρρέθη and ἐγὼ δὲ λέγω ὑμῖν shows how the people have been improperly trained by their leader to understand the Law, but Jesus is correcting that mistake. In particular, the religious leaders of Second Temple Judaism relaxed the absolute severity of the law (hence v. 19) by not penetrating beneath the plain surface of the words to the depths that the law requires. Jesus’ first example drives home this point through climactic parallelism in three parts:

πᾶς ὁ ὀργιζόμενος τῷ ἀδελφῷ αὐτοῦ ἔνοχος ἔσται τῇ κρίσει

ὃς δ’ ἂν εἴπῃ τῷ ἀδελφῷ αὐτοῦ, Ῥακά, ἔνοχος ἔσται τῷ συνεδρίῳ:

ὃς δ’ ἂν εἴπῃ, Μωρέ, ἔνοχος ἔσται εἰς τὴν γέενναν τοῦ πυρός.

Obviously, the structure of these clauses are similar, ending (gramatically) in ἔνοχος with a modifying phrase attached. So, in each case the person is liable, but to whom or to what he is liable grows. In the first clause, there is τῇ κρίσει, which is translated by many versions rather abstractly by “to judgment,” but my preference is for the NASB reading, “before the court.” Not only does BDAG support such a rendering, but v. 21 also indicates that the hearers would associate this with some specific judging body. They would all know where murderers stand trial, probably in the local court. Now, this probably struck them as strange. How would my local court know if I were angry, and why would they care?

With the second clause, the offense is more specific, an angry insult, and the judging body has grown to the Sanhedrin. Again, this was probably shocking, and by this point frightening, that a verbal outburst should cause someone to stand before the supreme court of the land. The point is getting clearer.

With the third clause, the offense seems to me to be about the same as the second, but the judgment is now unto (note the telic preposition εἰς) the Gehenna of fire. The meaning is clear: this person is liable to God’s heavenly judgment. Now, I’ve heard before, and I don’t know if it’s a common opinion, the idea that there is a corresponding climactic parallelism in the person’s sin by saying that Μωρέ was a particularly awful insult, something that would distinguish it from Ῥακά. I can’t find any real linguistic basis for this, but I see the reason why someone would want to suggest this, and it’s quite sad. Despite the whole point of this passage, the person who suggests such an interpretation is stuck thinking that little sins deserve little punishments and that really, really bad sins deserve hell.

The point of the anger passage, and the other examples to come, is that the Law demands absolute perfection. If human judges knew everything and were to judge by the absolute strictures of the Law’s intent, we would be beyond hopeless. Jesus is masterfully employing the evangelistic use of the Law, to pronounce condemnation for sin in preparation for Gospel (cf. Rom. 3:19-26).

Quickly, I’d like to point out one other thing that I’ve not heard stressed (though I’m sure someone has). The two applications in vv. 23-26 are introduced with an οὖν. This signifies a logical movement. That is, if we have understood that the Law prohibits not only outward sinful actions but also the inner thoughts and heart attitudes associated with and leading to them, we ought further to understand that the Law enjoins us to the opposite duty to the utmost of our ability (cf. Westminster Larger Catechism, 99). So, where such breaches may currently exist, we are obligated to do our duty to resolve them and to keep them from escalating.